Study on Geotechnical aspects related to rehabilitation of deteriorated sewer pipelines

在日本，许多安装在城市地区的旧下水道管道严重退化，降低了其功能，增加了地面凹陷的可能性。下水道不是压力管道。因此，如果旧管道恶化，土壤颗粒往往会随水流入管道，很容易在地面上形成空洞，导致地面下沉。然而，目前对地基中空洞发育的机理和实际情况尚不清楚。此外，由于在城市地区用新管道替换劣化管道的挖掘很困难，使用塑料内衬的非开挖修复方法已经开发出来，并在世界上越来越多地使用。塑料内衬寿命长，但由于松弛，其硬度会随着时间的推移而降低。相反，管道周围回填土的刚度随着时间的推移而增加。因此，土体与管道之间的相对刚度决定了埋地管道的力学行为会随着时间的推移而发生变化。然而，到目前为止，这一问题还没有被研究过。本研究旨在阐明老化旧排水管道周围地下孔洞的发展机理，并研究土-结构相互作用的长期变化。主要结论如下：1)通过管口入水的土壤发育了地下的空洞。空洞的位置在管道的上部，但不在管道的顶部。沿管道长轴方向的裂缝不会在地基中产生空洞。2)由于反复的车辆荷载，回填土视硬度降低，导致塑料管挠度增加。随着时间的推移，塑料管的松弛显著地加强了塑料管的挠度。

In Japan, many old sewer pipelines installed in urban areas were severely deteriorated to decrease their functions and increase the possibility of ground depression. Sewer pipes are not pressure pipes. If the old pipes are deteriorated, therefore, soil particles tend to flow into the pipes with water, easily developing voids in the ground to cause ground depression. However, mechanism and actual condition of void development in the ground have not been clarified yet. Also, since excavation for replacing the deteriorated pipes by new pipes is difficult in urban areas, no-dig rehabilitation methods using plastic inner liners have been developed and are increasingly being used in the world. The plastic inner liners have long lives, but their rigidity decreases according to the elapsed time due to relaxation. On the contrary, the rigidity of backfill soils around the pipes increases according to the elapsed time. Therefore, mechanical behavior of buried pipes that is governed by relative rigidity between soil and pipe will be changed according to the elapsed time. However, this problem has not been studied hitherto.This study was carried out to clarify mechanism of void development in the ground around deteriorated old sewer pipelines and to investigate long-term change in soil-structure interaction. The main conclusions can be summarized as follows:1) Inflow of soil through opening at joints of the pipeline develop the voids in the ground. The location of the voids is at the upper part of the pipe, but not at the top of the pipe. Cracks along the long axis of the pipe do not produce the voids in the ground.2) Apparent rigidity of backfill soils decrease due to repeated vehicle loading, resulting in increase in deflection of plastic pipes. The relaxation of plastic pipes during the elapsed time remarkably strengthens the deflection of plastic pipes.